1. Field of the Invention
This invention relates to a method and apparatus for the production of a biaxial woven fabrics.
2. Description of the Prior Art
The use of high performance woven materials is becoming increasingly common in applications such as aerospace and aircraft structural components. Particularly for use as reinforcing structures in forming rocket motor parts, heat resistant components as well as primary and secondary load bearing members it has become the material of choice. To provide the physical properties necessary to function in these demanding environments, these fabrics must be manufactured to great accuracy so that there is as much uniformity as is possible. A non-uniform woven fabric would create localized stress areas that would increase the possibility of a part failure. Misalignment of the warp or weft components cannot be tolerated in these applications. The fabric must be flat and uniform in appearance with no dense areas or voids. Generally, these high performance fabrics are manufactured from relatively flexible materials where mildly modified textile tooling does not produce a satisfactory product. In the normal weaving process, machines produce fabric from raw material (yarn, thread, etc. . . .). This raw material is generally made up of multiple strands of fiber that is bound in some way to create a rope-like consistency. The fiber is free to move in any direction desired, and in many cases the fiber can conform to any configuration. With this being the case, the weaving process is often very forgiving.
In a biaxial tape fabric, however, the materials used to form these fabrics are of a rigidized variety that have two fiber systems coming together to form the eventual woven fabric. The two fiber systems include warp fibers (0.degree.) and filling fibers (90.degree.). Woven fabric is a planar structure consisting of the warp and filling fiber which interlace at right angles. The mechanical weaving of biaxial tape material becomes increasingly difficult do to its radical differences from normal weaving materials. The major difference being the pre-processing that the raw material has undergone. Multiple strands of fiber are processed by impregnating the fibers with a resin to form a thin sheet of rigid material, followed by a slitting process to form a hard ribbon like tape. This strip is flexible in only one direction (up and down) and side-to-side movement is not possible while maintaining the flatness of the strip. Although the strip can be bent along its length quite easily, bends of less than 3/8 inch radius can result in fractures of the fibers thus making the normal weaving process impractical. This strip also lacks any elasticity, and is therefore unforgiving in the weaving process.
The basic weaving process that results in this interlacing is begun by first separating the flat sheet of warp fibers into two separate layers to form a "V" shaped opening which is called the shed. This "shed" is formed by raising and lowering of the harness frames which house the heddles that control the individual warp ends. Once the "shed" is formed, it becomes time to insert the filling fiber (90.degree.). The task of inserting the filling fiber is accomplished by the presentation of a long slender object with a clamping tip which is known as a rapier into and through the "shed" opening. When the rapier is fully through the "shed" opening, the filling fiber is presented and attached to the rapier tip so that the rapier can insert the filling fiber into the "shed" by pulling it through during its return trip to the beginning of its cycle. Conventional looms are designed to handle textile fibers which are very flexible and these flexible textile fibers can be presented to the rapier tip in a variety of out of plane configurations. However, with rigid strips, the filling strip (90.degree.) must be presented to the rapier tip in a flat plane. Conventional looms, at this point, would damage and deform the rigid filling strip, thus producing an unacceptable fabric. Furthermore, production breakdowns and overall less efficient production rates, with conventional equipment leads to a less economically efficient method, are more operator intensive and produce off-specification material.
Acceptable material requires that there be zero airspace between each individual fiber strip without creating physical damage to the material. Therefore, rigid flat fiber strips must be placed with precision into their respective orientation in a flat and uniform manner.
Therefore, there exists a need to provide a method and an apparatus for the efficient and economical production of rigid biaxial woven fabrics.